1. Field of the Invention
The present invention relates to fault circuit indicators. More particularly, the present invention relates to a microcomputer-based fault circuit indicator design.
2. Description of Related Art
Fault circuit indicators (FCIs) are typically installed at intervals along power distribution lines, or in proximity to critical loads. FCIs are installed for the purpose of providing fault indications when a fault has occurred downline, between the FCI and a next FCI or between the FCI and a critical load. In general, FCIs are well-known in the art.
U.S. Pat. No. 5,241,444 discloses a FCI that responds to a predefined increase in current over a given period of time (e.g., 50 amps over 3 cycles). However, the response is delayed in order to give a corresponding fuse or circuit breaker time to respond. The FCI then provides a fault indication only if it detects a subsequent loss of line current.
U.S. Pat. No. 5,168,414 also describes a FCI. In this patent, the FCI registers a fault in response to an overcurrent condition in an alternating current power distribution circuit, but only after a subsequent drop in the current level below a predefined threshold, which is essentially zero.
There are a number of problems associated with prior FCI designs, including the two FCIs described above. A first problem is that prior FCI designs base their fault indications on the detection of an overcurrent condition followed by a loss of current. This is problematic because backfeed and induced currents, particularly in three-phase systems, may prevent the current flowing through the affected line from dropping to zero. In fact, backfeed and/or induced current may not significantly differ from what might be considered a normal current level. Accordingly, prior FCI designs do not consistently indicate the presence of a fault condition when, in fact, a fault condition exists.
A second problem with prior FCI designs is that they are constructed exclusively with discrete electronic components. These components are not very reliable, particularly when exposed to extremely harsh environmental conditions. Consequently, these FCIs often fail, and replacing them is costly and especially inconvenient for utility companies providing power service to large, rural areas.
Yet a third problem associated with prior FCI designs is that they are not especially energy efficient. For example, the prior designs provide fault indications for a long period of time. This tends to drain the battery providing power to the FCI. Although the batteries can be replaced, doing so can be costly and inconvenient for the reasons presented above.
In view of the foregoing problems, there is a need for an FCI design that provides more accurate fault circuit indication, as well as one that is more reliable and more energy efficient.